Patent GB-1127742-A (GB)
Title: Improvements in or relating to image analysis systems
Inventor: SOAMES MICHAEL RICHARD
IPC: G01N15/14
Filed: 1965-02-06
Abstract: 1,127,742. Television. METALS RESEARCH Ltd. 28 Jan., 1966 [6 Feb., 1965], No. 5256/65. Heading H4F. To analyse and measure features contained within optical images a first scanned electrical video signal is derived from an optical image and the desired feature content is separated therefrom by signal level discrimination to form a second video signal, these two video signals are then compared and the discrimination level adjusted in response to the comparison so as to reduce to a minimum any differences between the two video signals in respect of the boundaries of the desired feature content. The two video signals may be applied simultaneously or sequentially to a conventional picture display monitor, the two images being superimposed or caused to appear in rapid succession so that they may be compared visually. Alternatively the two video signals may be applied to a monitor co-operating with switching means so that the image produced by the monitor comprises a plurality of parallel bands which alternately contain the image content of one or the other of the two video signals. In addition one or both of the video signals may be differentiated and phase inverted when necessary to provide unidirectional pulses so that only the feature boundary or outline signals remain in one or both of the video signals. In a further embodiment the two video signals are passed via pulse shaping means e.g. amplitude determiners or limiters 26 and 27, Fig. 4, and the second video signal is phase inverted 15 before it is combined 28 with the first video signal, the output signal being applied to a meter 32. The discrimination level of the discriminator 12 is adjusted so that the meter reading is reduced to a minimum. The image which contains only the desired features may then be analysed on a monitor (20). Alternatively the pulse shaping means 26 and 27 are preceded by analogue differentiating means (Fig. 5, not shown), whereby pulses are obtained which correspond to points on the boundaries of the desired feature of the original image. Further the pulse shaping means and analogue differentiating means may be replaced by an amplitude and a band width limiting means (38 and 40, Fig. 6, not shown) responsive to the second video signal, and quasi-differentiating means (42) and (43) are provided, one responsive to the first video signal and the other to the band width limited video signal which may be inverted before being combined with the first video signal and compared by means of a meter. The combining and comparing means may comprise switching means and amplifier means tuned to the switching frequency of the switching means, whereby the two signals may be sequentially presented to the amplifier, any difference between the two regions applied to the switching means appearing as an amplitude modulated fixed frequency A.C. signal, which may subsequently be amplified by the tuned amplifier. Although the difference may be indicated visually and the discrimination level adjusted manually a servo system may be provided which is responsive to the output from the meter. In a further embodiment the two video signals are applied to two monitors and an optical reflecting system comprising a rotating mirror or two half-silvered mirrors is provided so as to present the images from the two picture monitors either sequentially or in a superimposed manner on a suitable screen.